Three Yemeni nationals who were arrested in late 2003 say they were transferred to U.S. custody and kept isolated in at least four secret detention facilities that Amnesty International officials believe could be part of a covert CIA prison system.

The three detainees have not said they were physically abused while in U.S. custody, but they describe being whisked away in airplanes to unknown locations where they were interrogated by Americans in civilian clothes, according to an Amnesty International report. At one prison, the detainees were guarded by people in all-black "ninja" suits, who communicated using hand gestures.

During their separate incarcerations, the detainees were never visited by the International Committee of the Red Cross, never had access to lawyers, were unable to correspond with their families and had no contact with the outside world, the report said. Their families believed they were dead or were told that they had gone to Iraq to fight the United States.

The accounts, taken in independent interviews by Amnesty International researchers over the past few months, appear to be consistent with reports of a network of secret CIA detention facilities, according to the report. The detainees could not determine where they were because they were hooded during the flights, but because of the travel time they assumed they were in Europe or the Middle East, according to Amnesty International.

"We've tried working out where they might have been, but it's so subjective," said Anne FitzGerald, senior adviser on research policy for Amnesty International, who interviewed the detainees in two Yemeni prisons. "It's clear they were in facilities that were designed to hold many people, not just them. But they really didn't know where they were."

The CIA declined to comment Friday.

In a telephone interview from London last week, FitzGerald said she believes the detainees' stories are credible because they were each detained separately and were unable to communicate with one another before the United States turned them over to the Yemeni government in May. One of the detainees has never met the other two and is now kept in a separate facility, yet his story is consistent, she said.

Muhammad Assad was arrested in his home of Dar es Salaam, Tanzania, on Dec. 26, 2003, for alleged passport problems. A Yemeni native, Assad had lived in Tanzania for 20 years.

After his arrest and initial questioning, Assad was taken to a waiting airplane, and his family was told that he was deported to Yemen, according to Amnesty International. Yemeni authorities denied that Assad had entered the country, and Tanzania later informed Assad's father that he had been turned over to U.S. officials.

Assad believes he was arrested because of his connections to a charity that was "blacklisted" after the Sept. 11, 2001, terrorist attacks for allegedly funding terrorism. The al Haramain Islamic Foundation, a Saudi Arabian charity, had rented space in a building Assad owned. It is the only topic Assad was questioned about in his 15 months of incarceration.

He was first taken on a small airplane that flew for about two to three hours, and was interrogated for two weeks by Arabic-speaking people, according to the report. He was then flown elsewhere, a flight that he believes lasted about 11 hours, with a one-hour stop-over. When he arrived, his surroundings were much colder, and he was interrogated by white men who spoke what he believed to be American English.

"There was nothing haphazard or makeshift about the detention regime, it was carefully designed to induce maximum disorientation, dependence and stress in the detainees," according to the 20-page report. "The men were subjected to extreme sensory deprivation; for over a year they did not know what country they were in, whether it was night or day, whether it was raining or sunny. They spoke to no one but their interrogators, through translators, and no one spoke to them."

Salah Ali and Muhammad Bashmilah, who were living in Indonesia, were arrested in August and October 2003, respectively; Ali in Jakarta and Bashmilah in Amman, Jordan. They were taken to a Jordanian prison and tortured -- badly beaten and chained in uncomfortable positions -- by Jordanian authorities before being transferred to U.S. custody, according to Amnesty International. Both men had traveled to Afghanistan in 2000 to learn about jihad, but neither man fought against the United States, according to FitzGerald.

Ali said he was stripped and beaten with sticks by a ring of masked soldiers. "They tried to force me to walk like an animal, on my hands and feet, and I refused," Ali told Amnesty, "so they stretched me out on the floor and walked on me and put their shoes in my mouth."

Ali and Bashmilah recount similar stories after their transfer to U.S. custody in a place Amnesty International believes could have been Eastern Europe. They were put into a windowless, underground facility, each was isolated in a tiny cell, and their jailers and interrogators spoke English with American accents. In April 2004, they were moved to a new facility with "no pictures or ornaments on the walls, no floor coverings, no windows, no natural light," according to the report. It was here that the guards dressed in all black.

FitzGerald said that the two Indonesian detainees were barely interrogated after their first few weeks, perhaps an acknowledgment that they did not know much. All three were released to Yemeni authorities in May. Ali and Bashmilah are in the central prison in Aden, and Assad is at a security prison at Al Ghaydah. Their families now know they are alive, FitzGerald said.

"The cases of the three 'disappeared' Yemenis documented in this report . . . suggest that the network of clandestine interrogation centres is not reserved solely for high-value detainees, but may be larger, more comprehensive and better organized than previously suspected," the report says.

Such "incommunicado" detentions are against international standards but are consistent with recent reports of how the CIA operated its detention network.

Manfred Nowak, the U.N. rapporteur on torture, said in an interview last week that secret facilities are a particularly important issue because there is no outside oversight and no ability to know which detainees are in custody or where they are held. He condemned the practice.